Sensepoint XCD Technical Manual SPXCDHMANEN Issue 15
22
Power
The Sensepoint XCD transmitter requires a power supply from the controller of between 12 Vdc and
32 Vdc. Ensure that a minimum supply of 12 Vdc is measured at the sensor, considering the voltage
drop due to cable resistance.
The maximum loop resistance in the field cable is calculated as follows:
R
loop
= (V
controller
– V
detector min
) / I
detector
Example:
The controller is supplying a nominal 24 Vdc (V
controller
), the detector minimum allowable voltage is
12 Vdc (V
detector min
), therefore the maximum allowable voltage drop between the controller and detector
is 12 Vdc; this means a voltage drop of 6 V in each core (+ve core and -ve core).
Diagram 10 Power Connection
Power consumption of the detector is 5.0 W. The current required to drive the detector at the minimum
voltage is (I = P / V), 5.0 / 12 = 416.7 mA (I detector).
So, the maximum field cable loop resistance (R loop) = 12 / 0.42 = 28.8 Ohms, or 14.4 Ohms per core
(allowing for component variations, losses, etc.).
The following tables show the maximum cable distances between the controller and transmitter
assuming a voltage drop of 4V in each core and for different cable parameters. The tables are examples
only and actual cable parameters and source power supply voltage for the application should be used
to calculate the maximum cable distance allowed at the installation site.
Table 2 Maximum cable distances
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